In a Long Term Evolution (LTE) wireless system corresponding to an Evolved Universal Terrestrial Radio Access (E-UTRA) protocol formulated by the 3rd Generation Partnership Project (3GPP), a base station (referred to as an Evolved Node B, eNodeB, in the LTE system) on a network side may dynamically send, through a Physical Downlink Control Channel (PDCCH) or Enhanced Physical Downlink Control Channel (EPDCCH) or high-layer configuration signalling (for example, Radio Resource Control (RRC) signalling or Medium Access Control (MAC) signalling), or pre-configure a DownLink (DL) grant and an UpLink (UL) grant to User Equipment (UE) for the UE to acquire a resource of its Physical Downlink Shared Channel (PDSCH) or Physical Uplink Shared Channel (PUSCH). The UE receives the PDSCH or sends the PUSCH on the corresponding resource in a manner indicated by grant signalling according to the obtained DL grant or UL grant (or the preconfigured DL grant and UL grant).
The PDCCH and the EPDCCH are used for bearing Downlink Control Information (DCI). LTE initially adopts the PDCCH; however, because there exists stronger interference between different types of eNodeBs in a heterogeneous network, e.g., interference of a macro eNodeB to a pico eNodeB, and interference of a home eNodeB to a macro eNodeB, a UE-specific pilot-based multi-antenna transmission method for solving the abovementioned interference problem is put forward in a subsequent version of LTE. In addition, a PDCCH is mapped to a PDSCH area, and a frequency division multiplexing manner similar to that used in PDSCH multiplexing may be adopted to realize frequency-domain coordination of inter-cell interference. Such an enhanced PDCCH is called an EPDCCH.
Briefly, a Control Channel Element (CCE) is taken as a unit for a physical resource transmitted by a PDCCH, wherein the size of each CCE is 9 Resource Element Groups (REG), i.e. 36 resource elements, and each PDCCH occupies 1, 2, 4 or 8 CCEs. For the four kinds of PDCCHs respectively occupying 1, 2, 4 and 8 CCEs, aggregation in a tree structure is adopted, that is, the PDCCH occupying 1 CCE may be started from a location of any CCE, the PDCCH occupying 2 CCEs is started from a location of an even CCE, the PDCCH occupying 4 CCEs is started from a location of a CCE of which the sequence number is an integral multiple of 4, and the PDCCH occupying 8 CCEs is started from a location of a CCE of which the sequence number is an integral multiple of 8. Each aggregation level L, where Lϵ{1, 2, 4, 8}, corresponds to one search space, wherein there are two types of search spaces, i.e., a Common Search Space (CSS) and a UE-Specific Search Space (USS).
In the kth subframe, a control domain bearing a PDCCH consists of a group of CCEs, specifically, NCCE,k CCEs numbered from 0 to NCCE,k−1. UE needs to detect, in each non-Discontinuous Reception (non-DRX) subframe, a group of PDCCH candidates to acquire control information, the detection referring to decoding the PDCCHs in the group according to all DCI formats to be detected. A search space Sk(L) of an aggregation level Lϵ{1, 2, 4, 8} on subframe k is defined by a group of PDCCH candidates, and a CCE corresponding to PDCCH candidate m in the search space Sk(L) may be defined by a formula as follows:L·{(Yk+m)mod └NCCE,k/L┘}+i where i=0, . . . , L−1, Yk is an initial candidate location of a USS, NCCE,k is the number of CCEs for bearing the PDCCH in the kth subframe, m=0, . . . , M(L)−1, M(L) is the number of the PDCCH candidates to be detected in the search space Sk(L), and the search space consists of continuous CCEs; for a CSS, Yk=0, and L is valued to be 4 or 8; and
for the USS, L is valued to be 1, 2, 4 or 8, Yk=(A·Yk-1)mod D, where Y−1=nRNTI≠0, A=39827 D=65537 k=└ns/2┘, where └ ┘ represents rounding down, ns represents a timeslot number in a radio frame, nRNTI represents a corresponding Radio Network Temporary Identifier (RNTI).
The newly considered EPDCCH in LTE continues to use a framework design of a PDCCH as much as possible, concepts of an EPDCCH Enhanced CCE (eCCE) and the eCCE aggregation as well as a design of a search manner of an EPDCCH in an eCCE-set-based search space all continue to use the manners adopted for the PDCCH, and the only difference lies in the specific aggregation levels, the division of eCCEs and the change of resource locations of the EPDCCH to a new resource area.
The PDCCH or EPDCCH in LTE is distinguished by different types of DCI formats, and each DCI format and each information field in the DCI formats in LTE are defined in 3GPP TS 36.212, wherein DCI format 0 and DCI format 4 are used for UL grant; and DCI format 1, DCI format 1A, format 1B, format 1C, format 1D, format 2, format 2A, format 2B, format 2C and format 2D are used for DL grant. Each DCI format contains a 16-bit Cyclic Redundancy Check (CRC), and each CRC may correspond to an RNTI in an implicit coding manner, that is, the CRC is scrambled by the RNTI. The UE then performs blind detection on the PDCCH or the EPDCCH according to the RNTI to acquire its control information. RNTIs defined in LTE include Cell Radio Network Temporary Identifiers (C-RNTI), Semi-Persistent Scheduling Radio Network Temporary Identifiers (SPS-RNTI), Random Access Radio Network Temporary Identifiers (RA-RNTI), Paging Radio Network Temporary Identifiers (P-RNTI) and Temporary Cell Radio Network Temporary Identifiers (TC-RNTI), wherein the C-RNTI and SPS-RNTI are UE-specific, can distinguish UE and are identifiers allocated to the UE by a network.
The control signalling format for bearing a DL grant or a UL grant on a PDCCH or an EPDCCH in LTE is for single UE, that is, one PDCCH or EPDCCH signalling can be granted to only one piece of UE. Therefore, when there are many pieces of UE, overhead of the PDCCH is relatively high, and increase of the overhead will reduce data throughput of a system and namely reduce spectral efficiency. Under the condition that the overhead of the PDCCH is fixed, the number of the UE that can be scheduled at a certain moment is limited, then scheduling of a part of UE needs to be delayed, and the resource at the moment may also not be fully used, thereby causing influence on the throughput or user perception.
For the problem, there is yet no effective solution.